This is a documented On/Off Controller component with support for controlling Arduino UNO board output from a Unity game or application.

This asset supports an Arduino / Genuino UNO boards connected via USB serial and makes it possible to control the output signals on 5 digital/PWM pins - 3, 5, 6, 10 and 11 on the UNO.

This video explains how to use this asset with the Unity Animation window and Animator window to make a LED sequence light show that can be controlled from a Unity in-game UI. No code needed!